Microencapsulated phase change material suspension (MEPCMS) is a type of latent two-phase heat transfer functional medium capable of both energy storage and transport. For the anticipated practical application of the fluid, precise characterization of the viscosity characteristics of the suspension is vital, particularly in the process of phase transition. In this experiment, the paraffin phase change microcapsules with regular appearance, uniform particle size and density were prepared utilizing a three-phase coaxial microfluidic device. Five groups of phase change microcapsules, measuring 30µm, 50µm, 75µm, 100µm, and 125µm in outward radius, were prepared. Using a Malvern rotary rheometer, the dynamic viscosity-shear rate curve of MEPCMS was tested between 20s^-1 and 500s^-1; The transient viscosity-temperature curve of MEPCMS was tested from 15°C to 35°C and 35°C to 15°C under an unsteady state, and the dynamic viscosity under steady state was tested every 1°C.

Based on the tests performed, it was found that the viscosity of MEPCMS gradually decreases with increasing temperature and decreases with increasing particle size during the heating process in the single phase temperature range. The transient viscosity of MEPCMS is higher than the steady-state viscosity value in the region of the phase transition, where it first slows the rate of fall and then increases. As particle size increases, the average viscosity in the phase transition region decreases during melting. Unlike melting, the viscosity of MEPCMS gradually increases as the temperature decreases during the cooling process in the single-phase temperature zone, and the viscosity decreases as the capsule size increases. The transient viscosity of the suspension exceeds the steady-state viscosity value when the particle size is 30µm, 50µm and 75µm, but the transient viscosity of the suspension is less than the steady-state viscosity value when the particle size is 100µm and 125µm. In addition, the average viscosity decreases as the particle size increases.